Generally, keyboards are essential peripheral devices of computers. A keyboard is usually equipped with plural keys. By depressing one of the plural keys, the user can input a message or a command into the computer. Conventionally, different methods are provided to generate key signals according to the types of the keys. For example, in case that the key is a mechanical key, a metallic elastic strip is used to trigger a circuit switch to generate the key signal. Whereas, in case that the key is an optical switch key, a key switch signal is generated when a sensing light is received or obstructed.
In the conventional optical switch key, a light emitter and a light receiver are installed in the single key. When the light beam emitted by the light emitter is received or not received by the light receiver, the key switch signal is generated. However, since the light emitter and the light receiver are installed in the key, the structure of the key becomes more complicated. Moreover, it is difficult to adjust or correct the optical path. If the light emitter or the light receiver is defective, the entire of the key has to be replaced with a new one. That is, the maintenance cost is increased and the maintaining process is complicated. Moreover, the light beam in the key is easily influenced by other stray lights, for example the lights generated by a backlight module of the keyboard. Under this circumstance, the light beam is erroneously received by the light receiver, and thus the signal is misjudged by the light receiver. Therefore, the conventional optical switch key needs to be further improved.